The T-26 Soviet light tank was based on the British Vickers 6-Ton tank. The Vickers was one of the most successful tank designs of the 1930s. The Vickers design was copied and improved by the Red Army, becoming their most common tank up until 1941.

During the Spanish civil war of 1936-39, Republican Spain received 362 T-26 model 1933. This was by far the most important pre-WW2 combat experience for Soviet tanks and crews. The Republican T-26s completely outclassed opposing tanks in Spain, which usually had only machineguns as armament. These opposing tanks included the German Panzer I and the Italian CV-33/35 series. The T-26's 45 mm gun could easily destroy Nationalist tanks, and its HE shell gave it some ability to attack towed antitank guns. Nationalist units frequently succeeded in capturing abandoned T-26s and putting them into service in their own units.

The T-26, like most of the lightly-armored tanks of the 1930s, was vulnerable to mines and towed antitank guns such as the German 37 mm, Italian 47 mm, and Italian 20 mm. The experience of Spain led directly to the next generation of heavily-armored Soviet tanks such as the T-34 and Kliment Voroshilov.

In the Winter War, both sides used T-26s. As in Spain, the T-26s armour was found inadequate against towed anti-tank weapons. Dozens of these tanks were captured by the Finns and used until the end of WWII.

When Germany invaded the Soviet Union in Operation Barbarossa, the T-26 was the most numerous tank in Red Army units. The T-26 was the equal of the German Panzer 35(t) and Panzer 38(t) light tanks, and outclassed the still-numerous Panzer II. However, they were themselves outclassed by the German Panzer III and Panzer IV. More importantly, by June 1941 a high percentage of the T-26 fleet was old and in a very poor state of repair. Crews were not well trained and leadership was poor, leading to huge losses of tanks and men. Most of the remaining T-26s were abandoned or destroyed during 1941 battles of the WWII. They became relatively uncommon by mid-1942, when the few surviving vehicles were taken out of use.

A few T-26s were used by the German forces in anti-partisan operations far from the front lines.